Vehicles have been equipped with hazard warning lights for some time past. These hazard lights are operated by a dashboard control switch.
Operation of the conventional hazard switch will cause the conventional turn signals, in most cases, to flash simultaneously. In the case of a hazard the light are controlled by a hazard flasher light switch system. The hazard flasher and light switch are independent of the switches for the turn signals and overides them.
Usually the hazard lights are activated by the driver after the vehicle has come to a stop. When activated lights then flash on and off. If the vehicle (or the driver) develops a hazard while driving on the highway, the vehicle may come to a stop in a driving lane. This will cause a sudden emergency whether or not the hazard lights have been activated, and the vehicle will block a lane of traffic. This creates a dangerous situation. Flashing the hazard lights, alone, will not make the situation less hazardous, for the vehicle and driver, or for the traffic around it.
Preferably the vehicle (or driver) in trouble should move out of the traffic, onto the side of the road, thus leaving the driving lanes clear. This manoeuver, if the vehicle is controllable at all, can be difficult in heavy traffic, especially bearing in mind that it must be done after the hazard situation has arisen, when the driver may have difficulty controlling the vehicle, or the driver may become panicked or disoriented. The driver may feel that moving over a lane and attempting to leave the road creates a hazard in itself. The regular turn signals will not work, once the hazard flasher is activated. However, a vehicle in trouble may have no choice but to make such a lane change to get out of the traffic for its own safety and that of the passengers, and this may be an abrupt, unplanned move.
Indicating such a lane change with the conventional turn signals after the hazard lights have been activated, will be impossible. The hazard warning flasher overrides the turn signal control, since the hazard system flashes both lights simultaneously.
Thus the driver of a vehicle which is in trouble and who first activates the hazard lights, while driving, is prevented from being able to use the turn signals to indicate a turn or lane change, since the activation of the hazard lights cuts out the turn signal control. Clearly it is desirable to provide the driver with the option of being able to activate first the hazard lights in the conventional way, and then operate an emergency turn signal, or hazard turn light, indicating a turn or lane change in spite of the existing operation of the hazard light flasher. For many years, most vehicles are equipped with a third rear brake light usually mounted centrally on the back of the vehicle, and usually at a higher elevation than the side brake lights and turn signal lights.